A synthesis of Eurasian Curlew (Numenius arquata arquata) demography and population viability to inform its management

Abstract

The European population of Eurasian Curlew Numenius arquata arquata, a nearthreatened wader subspecies, has undergone pronounced population declines over the past 30 years. To assess the demography and viability of its global population, we surveyed studies quantifying demographic rates (productivity and survival) and complemented this review with new estimates of survival probability at the flyway scale. Then, using a demographic model, we estimated population growth rates while accounting for the range of variation of demographic parameters, and compared these estimates (expected based on demographic rates) with those observed based on population censuses. Both observed and expected average growth rates were negative but the observed rates were higher than estimates from demographic models (λ = 0.98–0.99 compared with 0.85–0.95). This discrepancy implies that there is geographical variation in the demography of different populations that is not fully covered by current demographic data, namely unstudied regions with higher productivity. According to our calculations, at the flyway scale, productivity is currently c. 0.57 fledglings per pair per year, higher than the average reported productivity of 0.29, but lower than the 0.68 needed to achieve a stable global population size (λ = 1). Adult survival, estimated at 0.90, was the most sensitive parameter determining population growth rates, but the low productivity levels over the last few decades seems to be the most probable cause of population declines. The negative population growth rates require immediate conservation actions to preserve adult survival and increase the extremely low productivity in western and northern European populations to values above 0.68 fledglings per pair per year. We hope our synthesis on the demographic status of Curlew in Europe will encourage the collection of more demographic data and allow concrete management goals at the flyway scale to be established in order to recover the global population of this iconic species.